DOI: 10.1002/chem.201001214 Biaxial Nematic Mesophases from Shape-Persistent Mesogens with a Fluorenone Bending Unit Matthias Lehmann,* [a] Christiane Kçhn, [a] Jo¼o L. Figueirinhas, [b] Gabriel Feio, [c] Carlos Cruz, [b] and Ronald Y. Dong [d] Nematic phases, applied in almost all commercial liquid- crystal (LC) displays, are LC phases with mesogens isotropi- cally distributed and exhibiting orientational long-range order of one preferred molecular axis along a common di- rection defined by the so-called director. These are the phases with the lowest viscosity and besides the anisotropic properties, are most similar to isotropic liquids. Biaxial nem- atics should realise a long-range orientational order of all three molecular axes along three mutually perpendicular di- rectors, but maintain the isotropic distribution of the molec- ular centres of gravity and their molecular mobility. Such phases are not only appealing from the viewpoint of basic research and theoretical modelling, but are also of techno- logical interest to speed up the switching of LC displays. [1, 2, 3] After the prediction by Freiser, [4] Saupe and Yu were the first to discover such mesophases in a narrow region of the phase diagram of a lyotropic LC. [5] The much-pursued syn- thesis of molecules for board-shaped mesogens, though suit- able for forming thermotropic biaxial nematic phases, did not, however, reveal a widely accepted biaxial mesophase. [6] Only recently, biaxial nematic phases of multipodes [7] and polymers [8] with side-on attached nematogens, the rotation of which about the long axis is hindered, could be con- firmed. In the area of low-molecular-weight mesogens, theory predicted V-shaped mesogens [1, 9] and mixtures of rod- and disc-shaped molecules [1, 10] as potential candidates for biaxial nematic phases. Indeed, the biaxial nematic phase at high temperatures, above 100 8C, was found in a series of oxadiazole derivatives, [11] the results of which were most widely accepted and confirmed. [12] We were interested in parameters controlling biaxiality in such phases and focused therefore on shape-persistent mole- cules 1 with a well-defined bending angle (Scheme 1), [12–14] which is supposed to be a principal parameter in theoretical predictions. [1, 9] They were designed to self-assemble exclu- sively in nematic phases owing to the substitution pattern of alkoxy chains. [13] However, only planar bending units with a dipole along the bisector revealed nematic phases. [15] [a] Prof. Dr. M. Lehmann, Dipl.-Chem. C. Kçhn Institute of Chemistry, Chemnitz University of Technology Straße der Nationen 62, 09111 Chemnitz (Germany) Fax: (+ 49) 371-531-21229 E-mail: Matthias.Lehmann@chemie.tu-chemnitz.de [b] Prof. Dr. J. L. Figueirinhas, Prof. Dr. C. Cruz IST, TU-Lisbon Dep. de Física, Av. Rovisco Pais P-1049-001 Lisboa; CFMC, Av. Prof. Gama Pinto 2, 1649-003 Lisboa (Portugal) [c] Prof. Dr. G. Feio CENIMAT/I3N, FCT-UNL, P-2829-516 Caparica (Portugal) [d] Prof. Dr. R. Y. Dong Department of Physics and Astronomy University of British Columbia Vancouver, B.C., V6T 1Z1 (Canada) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201001214. Scheme 1. General structure of V-shaped, shape-persistent fluorenone nematogens and definition of molecular axes N, M and L. Chem. Eur. J. 2010, 16, 8275 – 8279  2010 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 8275 COMMUNICATION